Differences in health and longevity across societies and (as Michael Marmot's observation indicates) within societies, are large and ethically disturbing. Several decades' research in epidemiology and social and biomedical sciences in many countries confirms that inequalities in health co-vary with inequalities in income, education, and other social attributes. Barriers to health care access are only one contributing factor. Although the literature on health disparities can be traced back to the work of Engels and Virchow in the mid-nineteenth century, the field has expanded rapidly in recent decades. Some key publications, beginning in the 1970S stimulated a vigorous research effort involving scientists from many disciplines and countries. Marmot's "Whitehall" studies, for example, showed that the health prospects of British civil servants correlate with their rank